The present invention relates to an electrical machine of the transversal-flux type according to the preamble to claim 1 (see WO01/78218 (ABB AB) and WO01/78219 (ABB AB)). The invention also relates to a use of such an electrical machine.
Conventional electrical machines operate according to the so-called longitudinal-flux principle, which means that the magnetic flux plane of each stator element is parallel to the direction of movement of the rotor. U.S. Pat. No. 5,177,142 (Von Zweygbergk) discloses an electrical machine that operates according to the so-called transversal-flux principle. This known machine comprises a rotating rotor with a number of permanent magnets and a stator with a corresponding number of stator elements that are arranged in such a way that the induced magnetic flux substantially follows a path perpendicular to the direction of rotation of the rotor. The known machine is characterized by a high power or torque density, that is, a large power or a large torque in relation to the volume or physical size of the machine is obtained. U.S. Pat. No. 5,177,142 discloses rotating machines of the transversal-flux type.
WO01/78218 and WO01/78219 both disclose a linear electrical machine of the transversal-flux type. The known machine comprises a stator with a plurality of magnetic flux conductors and an electric conductor that forms a winding extending in a closed winding path through each magnetic flux conductor. The machine also comprises a movable element with a number of permanent-magnet elements. The movable element describes a reciprocating motion in relation to the stator along a movement path in a space with a finite length. The closed winding path comprises a first current-carrying section extending essentially parallel to the movement path. Each magnetic flux conductor together with one of the permanent-magnet elements forms a closed magnetic flux circuit extending around the current-carrying section. The magnetic flux conductors are arranged in an alternating order with respect to the direction of the magnetic flux in relation to the permanent-magnet elements and the magnetic flux circuit, respectively.
As mentioned above, transversal-flux machines are characterized by a high power or torque density, that is, the power or torque that may be obtained is great in relation to the physical size of the machine. Further, the power in a transversal machine, contrary to that of a conventional electrical machine, is directly proportional to the number of poles of the stator and the rotor or the movable element. As shown in the above-mentioned WO01/78218 and WO01/78219, a transversal machine may be made very compact, that is, with a large number of poles in a relatively small machine. However, the high torque density of known transversal-flux machines is associated with a relatively low power factor, that is, both the machine and the control unit must be designed for relatively great dimensional outputs compared with their active rated powers. The reason for the low power factor is that known transversal-flux machines have a relatively great leakage of the magnetic flux, which results in a weak magnetic coupling between the stator and the movable element or rotor. The magnetic leakage, which is of a certain magnitude in all types of electrical machines, means that part of the magnetic flux disappears from the imaginary magnetic flux circuit without performing any work. The leakage thus deteriorates the efficiency of the machine.
In the above-mentioned electrical machines of transversal-flux type, leakage may arise both in the stator and in the movable element or the rotor. In the stator, leakage may arise between adjacent magnetic flux conductors in those sections where the magnetic flux extends in opposite directions in the adjacent magnetic flux conductors. In the rotor, leakage may arise between adjacent permanent magnets since these have a magnetic flux in opposite directions.